Lower olefins such as ethylene, propylene, and butene serve as important, principal raw materials for chemical industry. Particularly, various methods for producing propylene have been developed and modified actively in recent years, in expectation of significant growth in demand therefor. Propylene is mainly produced by the thermal cracking of naphtha or by the catalytic cracking of heavy petroleum distillate using a catalyst. Its reaction scheme is composed mainly of a fluidized-bed reaction using zeolite of USY or MFI type as a catalyst. These catalysts are sometimes inactivated due to heavy carbonaceous materials (coke) accumulating in zeolite pores as a result of reaction with hydrocarbon. Therefore, the catalysts require, for their regeneration, removing coke by combustion in an atmosphere containing oxygen. However, this coke combustion generates water which disadvantageously causes aluminum as an active site in the crystal lattice of zeolite to be eliminated from the crystal lattice, leading to reduced catalyst performance.
Moreover, the production of propylene using zeolite with methanol, ethanol (particularly, bioethanol produced with a plant as a raw material), or dimethyl ether as a raw material has also been studied as a method without the use of petroleum as a raw material. In this case as well, the dealumination of zeolite disadvantageously occurs due to high-temperature steam formed during this reaction, resulting in reduced catalyst performance.
For the purpose of overcoming these disadvantages or further improving the selectivity of an objective substance, a method for modifying zeolite with a phosphorus compound has been studied variously.
For example, Patent Literature 1 discloses a catalyst composition for fluid catalytic cracking of spherical hydrocarbon microparticles consisting of 5 to 20% by weight of P2O5, 10 to 50% by weight of zeolite of pentasil type, and 30 to 85% by weight of porous inorganic oxide, and a method for producing the same.
Moreover, Patent Literature 2 discloses a fluidized-bed reaction catalyst comprising pentasil zeolite, at least 5% by weight of P2O5, and at least 1% by weight of F2O3 and having an average particle size of 20 to 200 μm, and a method for producing the same.
Furthermore, Patent Literature 3 discloses a catalyst consisting of ZSM-5 and/or ZSM-11, phosphorus, and a substantially inactive matrix substance, the catalyst being used in a method for producing a light olefin and an aromatic compound from C4+ naphtha hydrocarbon, and a method for producing the same.